The present invention relates generally to dampers, and more particularly, to a thermal operator for use with such dampers.
A problem commonly encountered in conjunction with the use of many oil and gas fired home and hot water heaters, as well as wood and coal burning stoves and fireplaces, is that smoke and gases are constantly produced. These fumes must therefore be vented to the outside through a chimney or flue. This is done both to create proper draft conditions for combustion and to avoid creating conditions hazardous to the inhabitants of the building where such heating systems are being used. However, such a vent creates a permanent opening which, when the system is not being used, allows heat to escape from the structure being heated, creating the potential for considerable energy losses and, accordingly, considerable operating expenses.
In recognition of this problem, a variety of dampers have been developed which are capable of being fitted into the vent or chimney of the heating system to block this vent opening in a manner which conserves residual heat contained within the building, thus reducing the rate of fuel consumption. Essentially, such dampers generally use an external sensor to actuate the damper operator and thereby open or close the damper as needed. For example, U.S. Pat. No. 4,123,001, issued to Kolt, and U.S. Pat. No. 3,921,900, issued to Cole, both show bellows actuated systems for use with such dampers. U.S. Pat. No. 4,205,783 issued to Dietsch, discusses spring biasing means for use with a motor operated damper. However, the problems and expenses encountered in adapting such actuator systems to the damper and the associated chimney structure, as well as the cost of the power frequently required to operate such actuator systems, can be significant, often negating the savings afforded by the reduction of heat losses provided by the damper.
It is therefore preferable that the damper be self actuating, so that when placed into a vent or flue, the damper can respond directly and automatically to the presence or absence of heat or pressure to open or close. Using such a system, no external source of power would be required, providing a substantial savings in cost. Moreover, this permits such a damper to be located in plates where excessive heat loads exist, which can quickly degrade electrical sensor wiring, or where external power lines are difficult or expensive to install. Further, such dampers would be easier to adapt to a wide variety of operating conditions with a minimum of alteration or modification. Such capabilities can provide significant savings, both in the initial fabrication of the damper, as well as in the field installation and ultimate use of that damper.
One approach which has been used in an effort to meet this need for a self actuating damper involves the use of a plurality of interleaved bimetallic flaps, usually four, which are capable of reciprocally folding open and closed according to the ambient temperature within the flue. However, such a device tends to suffer from a number of disadvantages. For example, each flap must be self actuating, and therefore must be fabricated from relatively expensive bimetallic materials. Moreover, such materials, while flexible to some degree, are generally unable to completely fold out of the path of exiting smoke or fumes, thus creating a chimney restriction. This, at best, reduces furnace efficiency by reducing chimney draft, and at times, can even cause smoke and gaseous combustion products to back up within the system and escape into the building. Another disadvantage of such a damper is that the flaps must be specifically sized in order for the damper to be useful in a variety of applications. This adds to the normal scrap losses encountered in producing such a damper, adding significantly to its cost of production. Lastly, bimetallic material is relatively stiff. As a result, flaps manufactured using such materials do not respond quickly. Because of this, in furnaces where an increase in pressure can occur before an increase in temperature, for example in oil fired furnaces, such flaps are unable to open quickly enough to relieve the pressure produced. It is for this reason that such damper systems are not recommended for use with oil fired furnaces.
The foregoing disadvantages are further accentuated as the size of the damper is decreased to meet a particular installation requirement. Often, for relatively small dampers, the use of a plurality of folding blades or interleaved flaps is inappropriate, due in part to the precision required to manufacture the components of the damper, and to the amount of structure which must be encountered as air flows through the damper assembly. For this reason, single blade dampers are often used in such applications.
It is therefore desirable to provide a damper having a self actuating damper operator and which can be constructed of low cost, general purpose components, yet which is readily adaptable to a wide variety of installation situations and operational conditions. Such a system would significantly reduce, if not entirely eliminate, the foregoing problems.